Effect of Sn Addition on Thermodynamic, Dielectric, Optical, and Acoustic Properties of Lead Hafnate

Abstract

Specific heat, dielectric properties, domain structure, and Brillouin light scattering studies in antiferroelectric PbHf1−xSnxO3 single crystals with three different concentrations (x = 0.08, 0.1, and 0.23) are performed in function of temperature. The specific heat and dielectric data reveal clear anomalies at three temperatures denoted as T1, T2, and TC. At T1, transition from the antiferroelectric AFE1 to another antiferroelectric AFE2 phase is realized, the next phase transition (PT) is from AFE2 to an intermediate (IM) phase—at T2, and from IM to paraelectric (PE) phase at TC. PTs at T1 and T2 are definitely of the first order, whereas the PT at TC has features of the second‐order PT. The PT sequences are confirmed by changes in the domain structure. In the PE phase, Brillouin studies reveal the softening and broadening of longitudinal acoustic (LA) mode in the cooling process. The softening and broadening exhibit the maximum values near TC. The transverse acoustic (TA) mode appears near T2. Additional acoustic anomalies are also observed at T1. The temperature dependencies of LA mode indicate the existence of polar regions in PE phase and order–disorder character of the PT at TC. The other PTs are mainly of a displacive character.

Local properties and phase transitions in Sn doped antiferroelectric PbHfO3 single crystal

“…In our studies, we noticed that isovalent doping of PbHfO 3 by Sn ions produces effects similar to those of the hydrostatic pressure [24][25][26][27][28]. Such doping can be understood as chemical pressure since Sn 4+ ions have slightly smaller ionic radii.…”

“…The crystals were in the form of transparent, colorless plates of the surface of the order of 2 × 2 mm 2 and thickness in the regime 0.5-0.03 mm or thin needles with thickness ∼80 μm. Before the synchrotron x-ray and Mössbauer measurements, the crystals were characterized by measurement of dielectric permittivity, which we performed for the frequency of 100 kHz with the HP 4363 LCR meter, and by the calorimetric measurements that were made utilizing the Netzsch DSC F3 Maia calorimeter, in the same way, as described in [28].…”

“…In this work, we are going to demonstrate that the AFE2 phase in PHS compound is also incommensurate. The new IM phase develops between AFE2 and PE phases and its existence and temperature range depends on the concentration of Sn ions in PHS [28]. In this phase, large polar fluctuations were observed by Brillouin scattering experiments.…”

“…Small but clear thermal hysteresis noticeable on both ε(T ) and Δc p (T ), indicates for the I-order phase transition between two antiferroelectric phases. In our previous publication [28], it was established that the temperature range of the existence of particular phases depends strictly on the composition. Based on Raman scattering measurements, it was also determined that the mechanism of the AFE1-AFE2 phase transition is mainly of displacive mechanism for all compositions of PHS solid solution and even in pure PbHfO 3 [33][34][35].…”

The complexity of structural phase transitions in Pb(Hf0.92Sn0.08)O3 single crystals

“…20 In our studies, we noticed that isovalent doping of PHO by Sn ions (forming solid solution) produces effects similar to those of the hydrostatic pressure. [21][22][23][24][25] It is due to the fact that in PHS, a larger Hf 4+ ion (r = 0.71 Å) is replaced by a smaller Sn 4+ ion (r = 0.67 Å) in the central position in oxygen octahedra. Such doping can be understood as chemical pressure, since Sn 4+ ions have slightly smaller ionic radii.…”